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1991-01-13
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From wang!elf.wang.com!ucsd.edu!info-hams-relay Fri Jan 11 15:56:39 1991 remote from tosspot
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Message-Id: <9101111231.AA13518@ucsd.edu>
Date: Fri, 11 Jan 91 04:31:10 PST
From: Info-Hams Mailing List and Newsgroup <info-hams-relay@ucsd.edu>
Reply-To: Info-Hams@ucsd.edu
Subject: Info-Hams Digest V91 #51
To: Info-Hams@ucsd.edu
Info-Hams Digest Fri, 11 Jan 91 Volume 91 : Issue 51
Today's Topics:
2-meter J plans?
Cushcraft R5
Equipment servicing..
Giving out information (was Re: Radio Shack bashing
Radio Shack Bashing
spreadspectrum info wanted
WEFAX question and comments
Send Replies or notes for publication to: <Info-Hams@UCSD.Edu>
Send subscription requests to: <Info-Hams-REQUEST@UCSD.Edu>
Problems you can't solve otherwise to brian@ucsd.edu.
Archives of past issues of the Info-Hams Digest are available
(by FTP only) from UCSD.Edu in directory "mailarchives/info-hams".
We trust that readers are intelligent enough to realize that all text
herein consists of personal comments and does not represent the official
policies or positions of any party. Your mileage may vary. So there.
----------------------------------------------------------------------
Date: 11 Jan 91 08:31:30 GMT
From: uokmax!bateman@apple.com (Monte Bateman)
Subject: 2-meter J plans?
To: info-hams@ucsd.edu
Here are two articles I saved from about a month ago:
--- #1 from N6UBM ---
The following is a description of a J-Pole antenna made from 300 ohm
TV twin-lead. Quite a few of the hams in the area have successfully
built one or more of these antennas. They have quite a few advantages
which include improved performance for 2-meter HTs, portability, and
last, but never least, they are inexpensive.
| | do not short this end.
| |
| |
| |
| |
| |
54" | |
| |
| |
| |
| 1/4" gap
| |
| |
| | 16 3/4"
coax ctr conductor=>* *<= coax shield
| |
1 1/4" | |
-*-
solder the twin leads together at bottom
1. Start with 54 1/2" of TV twin lead (foam core does not work as well)
2. Strip 1/2" of insulation at bottom and solder wires together.
3. Measure 1 1/4" from soldered wires and strip insulation on both
sides. This is the solder point for a coax feedline.
4. Measure 16 3/4" from bottom and cut out 1/4" notch on one side.
5. Feed with a length of RG58U coax. Tape coax at feedpoint to the
twin lead for strength and weather protection.
I have also attached an alligator clip to the plastic on the top of
the antenna in order to conveniently hang it. I am successfully using
one in my attic to avoid any CCNR problems. I have another that I can
take with me camping, sailing, etc.
This design has appeared on many BBSs and in club newsletters; the
earliest reference that I know of is a Jan. 1984 D.A.R.C. antenna
article by James Burks, KA5QYV.
Enjoy,
N6UBM
--- #2 from John Keith, KD0GD ---
Here's a variation on the twinlead J-pole design that uses copper
tubing. The dimensions are a little different and the feed is different
from what has been previously posted but then that offers some
opportunity for experimentation (which is part of what amateur radio is
all about). I haven't personnally constructed one of these but I know
several local hams who have and they are very pleased with the results.
This makes a very unobtrusive and rugged antenna.
SIMPLE J POLE ANTENNA
The J-pole antenna offers good gain, compact size, simplicity and very low
cost. They are easy to build and compare very favorably against commercially
available antennas. As a side benefit they are DC grounded for lightning
protection. The construction style provides for a very durble antenna and one
that is very easy to mount. The total material costs should be about $10.
Material list:
1) One ten foot piece of 1/2" rigid copper tubing
2) One 90 degree elbow fitting
3) One T fitting
4) Two 5/8" rubber chair leg caps (or 2 copper end caps)
5) Two small stainless steel hose clamps
Construction: |
|
1) Cut the copper pipe to the following lengths |
(save the piece that is left over): |
57" (66 1/2" for a 5/8 wave) | 57"
19" | (66 1/2
3/4" (used to join the two fittings) | for 5/8
2) Using normal plumbing techniques (solder, | wave)
flux, torch) connect the tubing as shown | |
in the illustration. | |
3) Install either the rubber feet or solder 19" | |
the copper end caps in place. | |
90 elbow-> |---| <- T
Tuning: | fitting
|
1) Attach the hose clamps about 3" up from the | <- left
bottom of the "U" (5" for the 5/8 wave). | over
2) Attach the inner conductor of the coax to the
19" side and the braid to the 57" (66 1/2") side.
3) Check the SWR. Slide the clamps with the coax up
or down until a 1:1 SWR is achieved
If the copper color is not to your liking, paint it any color you wish. It is
strongly suggested that you use a good silicon compound to weatherproof the
coax connections against the elements.
---------
Note: I have not tried either of these antennas.
Hope this helps...
Monte
---
Monte Bateman
WB5RZX @ WB5RZX
bateman @ nsslsun.gcn.uoknor.edu
National Severe Storms Laboratory, Norman, OK! 73069
------------------------------
Date: 10 Jan 91 21:05:30 GMT
From: hpcc05!col!kenw@hplabs.hpl.hp.com (Ken Wyatt)
Subject: Cushcraft R5
To: info-hams@ucsd.edu
What's "tank coil tubing"? How would you like to lay out some
radials for me? The "soil" is decomposed granite! (Hi Hi).
------------------------------
Date: Fri, 11 Jan 91 10:28:42 GMT
From: "Pete Lucas, NCS-TLC, Holbrook House, Swindon" <PJML@ibma.nerc-wallingford.ac.uk>
Subject: Equipment servicing..
To: INFO-HAMS@ucsd.edu
>This reminds me....I have heard that if some minor part on the motherboard
>of your average clone computer fails (say a DIODE, which costs about 9 cents)
>that NO ONE who you take your PC to for repair will ever replace the
>diode. They always charge you for a NEW MOTHERBOARD, since a failure on
>the motherboard is regarded as too complex, and they never attempt
>component level troubleshooting on these things anyway.
>
>Is this true?
>
Quite often YES; it is cheaper to replace a whole motherboard (or disk
controller or whatever) then to have a repeat callout for the service
team. Remember in many instances the travel time costs more than the
parts used. Often, disturbing an old board increases the probability of
subsequent failure (disturbing old dry joints is not a good idea).
It is also easier for the repairer to offer a 90-day warranty if they have
fitted a whole assembly straight out of the box.
And then us hams get their hands on the 'dead' boards and replace the diode.......
Pete Lucas PJML@UK.AC.NWL.IA G6WBJ@GB7SDN.GBR.EU
------------------------------
Date: 11 Jan 91 07:48:00 GMT
From: usc!zaphod.mps.ohio-state.edu!sdd.hp.com!apollo!hays@apple.com (John Hays)
Subject: Giving out information (was Re: Radio Shack bashing
To: info-hams@ucsd.edu
I don't really mind giving the information out once in awhile, but sometimes
I'm in a hurry, I just want them to take my money, give me change and a
receipt and let me go. [I've already paid to much for the part, but Salt
Lake City isn't Silicon Valley -- I make a pilgrimage to Fry's whenever I
get to Santa Clara] --- On one occasion I said "My time is more important
to me, than your mailing list." (Politely, but I was in a rush) --- The
response was "you can shop somewhere else" (half under breath) and a receipt.
In the same store, on another occasion in the same store a middle aged woman
took the cleark to task over address info for a charge.
I know in the old days the stores used to get something like 2.5 cents a
name and address, so when I worked part-time at one store, I was supposed to
go through the phone book during slow periods and fill in names on
reciepts where people did not give the information (during slow periods).
Maybe someone should capture this whole thread and mail it to the CEO
of Radio Shack?
John KD7UW
------------------------------
Date: 11 Jan 91 03:10:31 GMT
From: hpcc05!col!bobw@hplabs.hpl.hp.com (Bob Witte)
Subject: Radio Shack Bashing
To: info-hams@ucsd.edu
Re: Radio Shack bashing
Is it too late to add rec.radio.shack so y'all have a nice quiet
place to complain about RS? Seems like this comes up every few months.
Bob, KB0CY
"If you don't like it, don't buy there. End of problem."
------------------------------
Date: 11 Jan 91 07:26:51 GMT
From: stevens%mpx1.lampf.lanl.gov@lanl.gov (Stevens, Thaddeus C.)
Subject: spreadspectrum info wanted
To: info-hams@ucsd.edu
Hello !!
I'm interested in experimenting with spread_sprectrum. Does anyone out have
any info on the following:
1. Can a narrow band FM tranceiver be modified to work spread ?
2. Does anyone make equipment for Ham use either ready made or kit form ?
I would appreciate replies posted so others that may have an interest.
Thanks,
Thad KG5ES
------------------------------
Date: 11 Jan 91 05:54:23 GMT
From: nsc!amdahl!netcom!mcmahan@decwrl.dec.com (Dave Mc Mahan)
Subject: WEFAX question and comments
To: info-hams@ucsd.edu
In a previous article, MEHARP01@ULKYVX.BITNET (Michael Harpe) writes:
>My problem with Taggart's design is that, while granted it's cheap (6809's can
>be had for $3 from surplus places) it doesn't take advantage of some of the
>newer graphics chips and microcontrollers that can be had. The demodulator is
>really cheap to build. It just uses a couple of op-amps and an A/D converter.
I have created a wefax decoder for the amiga computer, and my radio interface
is even simpler than that. I use exactly one LM339 comparator chip and some
resistors, a diode, and a few caps to provide the signal to my amiga. It seems
to work just great. I might be able to get better data if I were to throw in
a bandpass filter, but I doubt it. The CPU does all of the FM decoding, color
selection, and display on the standard monitor. It hooks up via the parallel
port on every amiga available today.
>I noticed someone commented about using a DSP system for this. That would
>ideal since you could program "software" filters and maybe even do enhancement
>right there in the DSP chip. Unfortunately, my math background is not nearly
>adequate to DSP (after I complete undergrad work, i'm going to do something
>about that) so mine won't have that. I'd like to see a DSP-based WEFAX decoder
>if someone does do one.
I am at the stage of adding image filtering to my program. I find that with
my radio/antenna system, most of the problems come about due to bursty noise
that is picked up and sent thru the radio to the computer. I plan to add
software to do a variety of filtering by using a 3x3 graphics kernal. This
method is a way for the program to do averaging, weighted averages, edge
enhancement, or transition enhancement. All you do to change the filter type
is to change the weights of the graphics kernal. If you are interested in the
technique, let me know via e-mail and I'll let you know how I plan to do it.
The idea is really a very basic and common thing in the image enhancement
world. The trick is to figure out how to do all the math in real time, as
this type of filtering (or any other filtering I'm aware of) is full of all
kinds of multiplications and additions. I plan on using lookup tables to
handle things quickly, especially the mulitplies and dividing required to
create the new pixel from received data. I haven't yet actually added the
filtering yet, so we will see if my ideas are really implementable. I
suspect that they are. Of course, the amiga really isn't too usable while
an image is being received.
>I think a WEFAX decoder is a great homebrew project. The project is complex
>enough to be challenging and yet can be done with fairly modest components and
>equipment. Taggart's book is required reading for this project.
Well, I haven't read his book because I can't seem to find it locally and he
doesn't answer my mail. I got all my info from asking questions on the net.
I would really like to get a copy of it, so if anyone knows of a mailorder
house that carries the latest version, please let me know. I agree that a
wefax decoder is really suited to homebrewing. Once the information is
gathered, it is a challenge (but quite doable) to design the hardware and
figure out how the software will work to display the image. Not everyone
can do it, but it is DEFINATELY not impossible for those that want to.
>Mike Harpe, N4PLE
>University of Louisville
-dave
--
Dave McMahan mcmahan@netcom.uucp
{apple,amdahl,claris}!netcom!mcmahan
------------------------------
End of Info-Hams Digest
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